Abstract
This paper presents a case study of driving speed at horizontal curves in the regional road. The literature review of operating speed at horizontal curves in regional roads expresses the difference between design speed and driving speed. Driving speed was measured in ten horizontal curves on regional road No. 2610. Collected data was compared to the design speed, various design standards, and Operating Speed Prediction Models for traffic in low-volume roads. Based on result analysis, was proposed initial adjusted minimum radius of the horizontal curve based on operating speed. It is justified that proposed corrections based on operating speed ensure a credible speed limit effect on road safety. The performed experiment showed different tendencies comparing measured driving speed with permitted and design speeds. It was determined that dependent on specific curved section drivers tend to exceed posted speed limit from 17% to 98% of cases, and from 41% to 100% − the design speed in the horizontal curve. This research led to identifying the limitations of experimental research methodology. These limitations are related to experimental Site selection with different combinations of alignment elements, traffic, and accident data. A pilot study showed significant results and gave essential insights into the full-scale research plan. The results are expected to benefit both other researchers and the organisations responsible for the development and implementation of normative technical documents for road design.
Highlights
In most countries, design guidelines of the road alignment include permissible speed (Vperm), design speed (Vd) and 85th-percentile speed (V85)
The goal is that Vd of the horizontal curve always be no lower than Vperm − posted speed
Limiting and standard values for most of the design elements are determined conforming to the Vd: maximum tangent lengths, minimum radii of the horizontal curve, minimum parameters of clothoids, maximum longitudinal grades and vertical curves
Summary
Design guidelines of the road alignment include permissible speed (Vperm), design speed (Vd) and 85th-percentile speed (V85). Individual alignment design elements are unrelated to Vperm. The goal is that Vd of the horizontal curve always be no lower than Vperm − posted speed. Limiting and standard values for most of the design elements are determined conforming to the Vd: maximum tangent lengths, minimum radii of the horizontal curve, minimum parameters of clothoids, maximum longitudinal grades and vertical curves. It is desirable that the driving speed of a large proportion of drivers be lower than the Vd (AASHTO, 2018). Significant differences in speed results in an increase in the frequency with which vehicle drivers pass one another, increasing the number of opportunities for multivehicle crashes. It is impossible to collide if the same speed is maintained
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